The prefrontal cortex is the region of the brain located just behind the forehead. This is where higher-level cognition occurs, such as recalling whether a word was heard aloud or read. Most people show evidence of more processing on the right side of the cortex. However, research has shown that many elderly people use both hemispheres more equally, thus processing bilaterally.

This discovery led to two opposing theories as to why. One theory supposes that this change in the prefrontal cortex is part of the general decline of the body, that bilateral processing is evidence of malfunctioning. The other theory supposes that enlisting the help of the other hemisphere of the prefrontal cortex is a way to compensate for reduced capacity in the more active hemisphere; that is, the brain is making up for its own failings.

Scientists conducted a range of cognitive tests with older adults in their 60's and 70's. They then chose two smaller groups from those subjects--those who performed high on the tests, and those who performed low. Then, while the subjects' brains were PET scanned, the scientists administered two of the same tests to the two groups of older adults, as well as to a group of young adults between the ages of 20 and 35. They found that the high-performing older adults showed significantly more use of bilateral processing than anyone else.

The research supports the theory that bilateral processing is a way to compensate for reduced capacity of the right hemisphere with age. Further research may examine how training individuals or using drugs to enhance bilateral processing affects diseases such as Alzheimer's.